The present invention relates to a device for measuring at least one parameter of a medium flowing in a line.
German Published Patent 197 35 891 Application No. describes a measuring body, insertable into a clean channel of an intake line of an internal combustion engine, for determining the mass of the intake air, which has a flow channel and a measuring channel that is essentially inclined in relation to a longitudinal axis of a line, and which subdivides into an S-shaped deflection channel adjoined thereto. A measuring element is arranged in the measuring channel. The measuring element can be constructed as a micromechanical sensor part having a dielectric membrane, as is known, for example, from the German Published Patent Application No. 43 38 891 and U.S. Pat. No. 5,452,610, respectively. Because of the entry of water into the intake line, for example, due to a roadway wet from rain, the measuring element may become contaminated. Natural components of dissolved salts contained in this spray water then cause a drift in the characteristic as the result of the buildup of salt crusts on the membrane of the sensor part. It may be that the inclination of the measuring body forms a screened region, however, dirt or liquid particles nevertheless get into the measuring channel.
From German Published Patent Application No. 197 35 664, a device is already known in which the measuring element is positioned within a tubular member through which the medium flows, an upstream end of the tubular member extending into a filter chamber, and there having inlet openings on a lateral surface to reduce the action of dirt particles or water droplets on the measuring element. Particularly in the case of heavily polluted air and a high water content in the intake air of the internal combustion engine, the danger exists that the air filter will become saturated with water which then passes through the filter mat and, in so doing, takes along dirt particles. On the downstream side of the air filter, the actual clean side, the danger now exists that the intake air will again carry along dirt particles and water droplets from the filter surface which then deposit in an undesirable manner on the measuring element, and which lead to measuring errors or a malfunction of the measuring element. By the arrangement of the inlet openings on the lateral surface, the tubular member according to the related art reduces the danger of deposits on the measuring element; however, a correspondingly long design of the tubular member causes an undesirable pressure drop which leads to a decrease in measuring sensitivity. In addition, given a fluid entry of 20 liter/hour resulting during operation of a motor vehicle, the reduction of the action of liquid/solid-matter particles on the measuring element is too small.
German Published Patent Application No. 196 52 753 describes a device having a measuring element, the device containing a flow rectifier and a grating for stabilizing a measuring signal. However, no further grating or element is used to protect the measuring element from liquids or solid-matter particles.
It has furthermore been proposed to use a repelling grating in a line to separate liquid particles from streaming air or a gas. Such a repelling grating, connected upstream of an inner pipe or in the line, influences the air/water mixture streaming toward the measuring element in such a way that the liquid particles are guided to a pipe wall or a line wall, while the air remains in a center of the inner pipe.
A different characteristic appears in response to the throughput of a mixture with air and dust in the line. Because of its still higher inertia compared to a liquid, the dust, in response to a change in the direction of flow forced by the side walls employed, changes its path only by reflection at the side wall, the principle of angle of incidence equal to angle of reflection being valid. Depending on the orientation of the side wall and the point of impact, a certain particle rejection thereby results, that is to say, a certain portion of the particles striking on the repelling grating is deflected by a reflection in the direction of the wall. The remaining part, after two reflections at the side walls, once more exhibits the main flow direction, and thus can strike, unhindered, on the measuring element downstream of the repelling grating.
In comparison, the device of the present invention has the advantage that the deflection of solid-matter particles and liquid particles is improved in a simple manner by varying the orientation of the side walls with respect to the main flow direction over their extension in the main flow direction.
It is advantageous to influence the path of motion of the solid-matter particles in the streaming medium by the formation of the side walls in such a way that it runs past the measuring element, since in this manner, the measuring element is not soiled.
The possibility of positive or negative angles of intersection of the side walls with the flow direction has the advantage that it permits more variations in the design.
The continuous curve of a channel has the advantage that the danger of a separation of the flow possibly arising is reduced, whereby otherwise an increased signal noise is caused.
The use of a tubular member in the line of the device has the advantage that additional protection is attained for the measuring element.